The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with dis-closures not known to the relevant art prior to the present invention but provided by the invention. Some such contributions of the invention may be specifically pointed out below, whereas other such contributions of the invention will be apparent from their context.
LTE defines an optional sounding reference signal (SRS) feature in the uplink. The sounding reference signal (SRS) is transmitted by UE by using a known sequence, similar a UL demodulation reference signal (DMRS), so eNB may use it to estimate UL channel quality. UL information may be decoded in eNB with UL DMRS. UL DMRS is transmitted from UE to eNB together with the UL data and both locate exactly in the same resource blocks, so the channel information eNB extracts from UL DMRS is for that transmission. SRS may be located in a UL PHY frame such that it is transmitted in the last symbol of a sub-frame if scheduled. SRS is used by the base station to estimate the quality of the uplink channel for large bandwidths outside the assigned PUSCH span to a specific UE. This measurement cannot be obtained with the DMRS since these are always associated to the PUSCH or PUCCH and limited to the UE allocated PUSCH or PUCCH bandwidth. SRS may be transmitted e.g. in every second sub-frame or as infrequent as every 16th frame. SRS may be transmitted on the last symbol of the sub-frame. The channel quality estimate may be obtained within a single SC-FDMA symbol.